Gramicidin is a polypeptide antibiotic mixture of gramicidin A , gramicidin B, and gramicidin C originally isolated from B. brevis. It is also a component of the antibiotic tyrothricin . Gramicidin is active against the Gram-positive bacterium S. aureus but not Gram-negative E. coli. It also protects mice from Pneumococcus infection in vivo when administered at a dose of 0.002 mg/animal. Gramicidin inhibits growth of bacteria by forming pores and channels in the cell wall, which increases its permeability to monovalent cations. Formulations containing gramicidin have been used as topical agents in the treatment of bacterial skin infections.
White, crystalline platelets. Soluble in lower alcohols, acetic acid, and
pyridine; moderately soluble in dry acetone and
dioxane; almost insoluble in water, ether, and
hydrocarbons. Depresses surface tension, forms a
fairly stable colloidal emulsion in distilled water.
Gramicidins are a family of linear pentadecapeptides isolated from Bacillus brevis by Dubos at the Rockefeller Institute in 1939. Gramicidin is a complex of six closely related analogues A1, A2, B1, B2, C1 and C2 where A1 and A2 are the dominant components. Gramidicins act by forming channels in cell membranes causing ion leakage, and is an essential bioprobe for understanding the nature of the cell membranes.
Medicine (antibacterial).
Targets primarily the cell membrane of Gram-positive bacteria and shows little effect against Gram-negative bacteria. Gramicidin is typically used as a topical antimicrobial agent because it also causes hemolysis of red blood cells.
An antibiotic produced by the metabolic processes of the bacteria Bacillus brevis. It is a polypeptide that is active against most Gram-positive pathogenic bacteria. It is one of the two antibiotic components of tyrothricin but has been isolated and used
Gramicidin is highly active against many Gram-positive bacteria.
Neisseria spp. are relatively resistant. Gram-negative bacilli including
Pseudomonas aeruginosa are susceptible although conflicting data exist
about the degree of susceptibility. Gramicidin has a bactericidal activity against Mycoplasma
spp. and several pathogenic fungi, including Candida albicans.
Interestingly, it also appears to have antiviral activity against HIV
and herpes simplex viruses (HSV-1, HSV-2).
Gramicidin is obtained from tyrothricin, a mixture ofpolypeptides usually obtained by extraction of cultures of B.brevis. Tyrothricin was isolated in 1939 by Dubos in aplanned search to find an organism growing in soil that wouldhave antibiotic activity against human pathogens. With onlylimited use in therapy now, it is of historical interest as thefirst in the series of modern antibiotics. Tyrothricin is a whiteto slightly gray or brown-white powder, with little or no odoror taste. It is practically insoluble in water and is soluble in alcoholand dilute acids. Suspensions for clinical use can beprepared by adding an alcoholic solution to calculatedamounts of distilled water or isotonic saline solutions.
Gramicidin acts as an ionophore in bacterial cell membranesto cause the loss of potassium ion from the cell. Itis bactericidal.Tyrothricin and gramicidin are effective primarilyagainst Gram-positive organisms. Their use is restricted tolocal applications. Tyrothricin can cause lysis of erythrocytes,which makes it unsuitable for the treatment of systemicinfections. Its applications should avoid direct contactwith the bloodstream through open wounds or abrasions. Itis ordinarily safe to use tyrothricin in troches for throat infections,as it is not absorbed from the GI tract. Gramicidinis available in various topical preparations containing otherantibiotics, such as bacitracin and neomycin.
Pharmaceutical Applications
Gramicidin as used in topical formulations is a mixture of
several closely related compounds, of which about 80% is in
the form of gramicidin A. It is part of the tyrothricin complex
originally isolated from B. brevis.
It is active against most species of Gram-positive bacteria,
including mycobacteria. Gram-negative bacilli are completely
insensitive.
It is highly toxic to erythrocytes, liver and kidney, and is
used only in topical formulations, usually as one of several
components.
Linear polypeptide antibiotic mixture of gramicidin A, B, C, and D. Gramicidin A acts as neutral carrier and helps in the establishment of ion flux across the lipid bilayer.
The mechanisms of gramicidin’s bactericidal activity have not been
fully elucidated. Gramicidin is known to alter the function of the
bacterial cytoplasmic membrane by forming channels that destroy the
ion gradient and make it permeable for inorganic cations . It may also be a potent and
specific inhibitor of the transcription reaction and inhibit the binding
of DNA-dependent RNA polymerase (transcriptase) to DNA .
Gramicidin appears to have antiviral activity against HIV, HSV-1,
and HSV-2 viruses and is also used as a
contraceptive due to its spermostatic properties.
The use of gramicidin is restricted to topical applications on wounds or
as ear and eye drops. Currently, much research is being invested to
generate less toxic analogs that still exhibit the same wide range of
bactericidal activity. To date, no new gramicidin-like polypeptides are
available for clinical use.
Gramicidin is used in some countries as a topical contraceptive,
because it has spermostatic activity.
